[Fot] TR6 Piston / Head Clearance

Fri May 27 10:59:58 MDT 2016

This discussion has been about flat top pistons to this point Tr6 and TR4
but what about our lonely little GT6s? Is it possible to get some decent
compression with flat tops in a GT6?  By decent I guess I'm saying I  would
like to see 11.5:1 or more.. To date everyone has suggested using dome tops
with all sorts of different configurations but if it were a simple matter
of raising the flat tops up into the combustion chamber it would make
matters much simpler. I know the heads are basically a TR6 head that has
been milled down about 1/4 of an inch so most of what would have been used
to shrink the combustion chamber size  is already gone. I also know that
with the TR6 head it's possible to "Flycut" or "Counterbore" into the head
for the piston to stick up quite a bit. Will this work with a GT6 head?
  Thanks. P.J.

On Fri, May 27, 2016 at 9:45 AM, Steve Yott <tr4 at wi.rr.com> wrote:

> Since most of you like to play the “death with pistons” game keep in mind
> one additional factor as you are building your engines.  Over the years I
> have found crankshafts which were reground and the throws were not very
> precisely indexed.  When a crank is setup on the grinding machine for
> grinding rod journals it is set and reset by the number of “throws”… on a 4
> cylinder engine the grinder has to be indexed twice and on the 6 cylinder,
> 3 times.  If the grinder, either the person or the machine is not perfectly
> accurate you will see variations of TDC for the throws!  I have seen these
> deviations be as much as .006” when a good grinder will hold dimensions
> within .001”.
>
>
>
> So, if you are running close squishes…. Measure TDC on #1 and #2 on the
> four cylinder and #1, #2 and #3 on the 6 motors….. this way to can make
> sure your throws and TDC’s are spot on.
>
>
>
> Steve Yott
>
>
>
>
>
> *From:* John Styduhar [mailto:johnstydo at gmail.com]
> *Sent:* Thursday, May 26, 2016 4:32 PM
> *To:* Gregmogdoc at surfnetusa.com
> *Cc:* Charly Mitchel; Steve Yott; Jim Gray; Triumph 'Friends of Triumph
> *Subject:* Re: [Fot] TR6 Piston / Head Clearance
>
>
>
> My forged pistons are .006" in the hole at TDC and I use a .030" thick
> solid copper head gasket and stock crank at 6200 rpm. When removing the
> head, the piston tops are clean in the squish area and it looks like a
> slight indentation at the ledge of the combustion chamber, probably from
> piston rock when the engine is cold.
>
>
>
> On Thu, May 26, 2016 at 3:23 PM, Gregmogdoc at surfnetusa.com <
> Gregmogdoc at surfnetusa.com> wrote:
>
> IN our experience with TR-4, and English Ford Kent
> racing engines the safe clearance between the head
> and the piston crown is .035".  A TR-4 with billet
> rods will just "touch" the head at 6800 rpm with
> .026" clearance. It will "hit" the head hard enough
> to make an imprint in the piston crown at .029"
> I would say that the TR-6 crank probably flexes more
> than a TR-4 does at high rpm. You would like to have
> a little safety margin, I would think. I would not
> run less than .035", maybe even a couple more if the
> engine is going to run over 6,000 rpm.
>
>
> Greg Solow
> The Engine Room
> Sports Car Specialists
> Santa Cruz, CA 95060
> 831 429-1800
>
>
>
> ------- Original Message -------
> From    : Charly[mailto:charly at mitchelplumbing.com]
> Sent    : 5/25/2016 6:52:35 PM
> To      : tr4 at wi.rr.com; toodamnfunky at comcast.net
> Cc      : fot at autox.team.net
> Subject : RE: Re: [Fot] TR6 Piston / Head Clearance
>
>  I tried b u idling a TR6 motor with a pop-up on the
> piston on c e. Instead of having the pistons cut
> down to zero clearance I left them about .005" high.
> It eventually bent the rod and broken it. The
> pistons had an imprint of the combustion chamber on
> them. I learned that at 6000 rpm's, there is
> enough deflection in the crank to let them hit the head.
> I believe most head gaskets are .0035" aren't they?
> Charly Mitchel
> TR6 #44
>
> On Wed 25/05/16 11:31 AM , toodamnfunky at comcast.net sent:
> > The rattling is likely piston slap on cold forged
> pistons. Did it go
> > away when it warmed up and came back on the next
> cold start ?jim
> >
> > -------------------------
> > FROM: "Steve Yott"
> > TO: "Robert Lang" , "FOT List"
> > SENT: Wednesday, May 25, 2016 11:27:27 AM
> > SUBJECT: Re: [Fot] TR6 Piston / Head Clearance
> > I doubt that your .030 squish would cause the
> rattling as you
> > describe.  The deflection caused by the crank, rod
> and piston in order
> > to hit the head at .030 would be way up in the
> rpm’s like 8000!
> > Did the rattling go away after all the parts warmed
> up and oil was
> > well disbursed or is it still rattling?  My first
> guess would be
> > either the engine was not pre-oiled or you have
> loose piston pin
> > bushings….  Were the rods rebuilt with new bushings
> fitted to about
> > .0003?
> > Steve Yott
> > FROM: Fot [ mailto:fot-bounces at autox.team.net ] ON
> BEHALF OF Robert
> > Lang
> > SENT: Wednesday, May 25, 2016 11:29 AM
> > TO: FOT List
> > SUBJECT: Re: [Fot] TR6 Piston / Head Clearance
> > Hi,
> > Where I was going with the query was this: I had a
> late block
> > "decked" with the intent of making the deck flat.
> The machinist took
> > of .032 to accomplish the goal. With a head gasket
> installed and the
> > head torqued, the clearance in the squish area is .030.
> >
> > I had initially wanted only about .025 removed, but
> we had to shave
> > an extra .007 to get rid of the fire ring cuts.
> >
> > On initial startup, the motor sounded like it might
> be "rattling" and
> > I'm trying to figure out why.
> >
> > When I used a stethescope on the block, everything
> sounds okay - no
> > rapping and the valve train sounds "normal" and
> there were no weird
> > sounds coming from the crank.
> >
> > I guess where I'm going with this is: if piston /
> head clearance is
> > too tight, I'll see some sort of indication on the
> piston, right?
> >
> > TIA for any sage advice.
> >
> > This is my first experience "decking" a block. I'd
> like to get it
> > right, I don't have the resources to start a new
> block from scratch.
> >
> > Regards,
> >
> > Bob Lang
> > _______________________________________________
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